The invention concerns a storage battery that is protected against the discharge of acid, with a compressible, microporous, and capillary separator material disposed between the electrode plates. This material completely fills up the space between the electrode plates and absorbs the electrolyte that is present in the storage battery cell. Such storage batteries are known, for example, from the German Patent Specification DE-OS No. 31 06 203.
The separator material consists of microfibers, e.g. microglass-fibers, which have been processed into mats or fleeces and which are offered commercially as strip goods in rolled form (e.g. AGM=Absorptive Glass Mat from Evants Products Company, U.S.A.)
As regards the arrangement of the separator material between the negative and positive electrode plates, it is considered important that the separator material contacts the plates completely and with an intimate contact, so that the surfaces of the electrode plates are adequately supplied with electrolyte in their entirety, for the electrochemical processes. To improve this contact, the plate sets with the separator material in between are built into the storage battery cells in a tight-fitting fashion, i.e., under a certain passage, during the manufacturing process of the storage batteries. However, this requires greater care in the assembly and production process, since the compressible separator material may not be compressed too severely over its entire surface or in local component areas. Otherwise, its capacity for taking up electrolyte is reduced, or shortcircuits can occur between the positive and negative electrode plates.
To maintain a certain minimum distance between the electrode plates, the German Patent Specification DE-AS No. 11 94 015 already proposed to encase the individual electrodes with a fleece material, and to dispose spacers between the electrode plates, which cause the fleece material to lie against the electrode plates and simultaneously maintain the electrode plates at a distance with respect to one another. However, it was presupposed that each plate had its own fleece encasement, so that the spacers could be disposed between the encased plates. The intermediate space between the encased electrode plates, which was bridged over by the spacers, thus remained free of separator material.
However, this technique is not useful for storage batteries that are protected against the discharge of acid, of the type mentioned in the introduction, since here the space between the electrode plates must be completely filled up with a microporous separator material. Also, the mechanical handling of the separator material, as proposed in the German Patent Specification DE-AS No. 11 94 015, would not be feasible with the storage batteries according to the type described here, since the required and actually used microporous mass of fleeces had very fine fibers and mechanically can sustain no stress at all. They already tear under simple mechanical handling and, especially in the mass production of starters batteries, cause considerable breakdowns both in the manufacture and in the operation of the storage batteries.
The aim of the invention therefore is to propose a teaching for the technical handling of storage batteries of the type defined in the introduction. This teaching will show how, despite the required use of a microporous and mechanical unstressable separator material, one can guarantee consistent production quality and a shortcircuit-proof operation of the storage batteries.
According to the invention, this aim is achieved by spacers being present between the electrode plates, in a manner that is in itself well known, but where the spacers are built into the separator material during a preliminary production step of the separator material, and where said spacers have support surfaces which are situated at least on one side of the separator material below the surface of this separator material, and which preferably extend approximately parallel to the surface of the separator material. Here, a suitable embodiment of the invention provides that the support spacing of the support surfaces of the spacers is up to 70% but preferably 20% to 50% smaller than the thickness of the uncompressed separator material, and thus the support surfaces of the spacers clearly lie below the surface of the separator material either on one side or on both sides of the separator material.
A storage battery according to the invention can be fabricated without any problem, and specifically even if the electrode plates with the separator material in between are multiply stacked above one another during the production process. The spacers that are integrated into the separator material prevent the undesirable strong compression of the highly porous separator material. Optimal contact between the pasting compound of the electrode plates and the separator material exists if, according to an advantageous development of the invention, the support spacing of the support surfaces is scaled in such a way relative to the thickness of the uncompressed separator material, that, after compression of the plate set, the separator material contacts the electrode plates with a defined surface pressure of maximally 80 kg/dm.sup.2 but preferably 20 to 60 kg/dm.sup.2. Here, the prescribed plate spacings are adhered to exactly.
This is also true if slightly bent or distorted electrode plates must be processed during the production process. Such plates occur again and again, for example, due to special conditions during casting the grid plates or during formation of the plates. Up to now, the bent or distorted plates had to be removed from the production sequence and had to be aligned, with considerable effort; otherwise, there was a risk that the excessively compressed separator material in the area of the distortion or bending would favor lead dendrites going through from the negative to the positive electrode plate. This could cause a shortcircuit between the electrode plates already after a few working cycles.
Now this danger has been eliminated. In the manufacture of the storage battery according to the invention, distorted or bent plates are aligned flat through the spacers that are built into the separator material. This happens automatically when the sets of plates are stacked. Thus, the prescribed plate spacings are adhered to exactly over the entire surface of the electrode plates.
It is here of special importance that the spacers with their mechanical action are not supported directly against the electrode plates, at least on one side or preferably on both sides, but have their support surfaces lying within the separator material, so that sufficient separator material is present between the support surfaces and the plates. In this way, electrolyte will be conducted to the plate surfaces, and oxygen can adequately diffuse to the negative plate surface even in the region of the spacer. This is improved still further if, according to an advantageous embodiment of the invention, the spacers consist of a porous and preferably highly porous material, such as, e.g. a porous sintered body or a porous hard foam.
The fact that the electrolyte is guaranteed to be conducted to the entire plate surface, in combination with the exactly maintained plate spacings, now also makes it possible to fabricate without any problem high-power batteries that are leakproof against the discharge of acid. With high-power batteries, one strives for plate spacings of only 0.5 mm, which can actually be achieved according to the inventive teaching.
The spacers that are built into the separator material have a support surface, e.g. over the entire area or in the form of a support cross, which extends preferably about parallel to the surface of the separator material and thus parallel to the plate surface. In this way, an undesirable excessive compression of the separator material that is situated before the support surfaces, as well as the undesirable penetration of the support surfaces into the relatively soft pasting compound of the electrode plates, is prevented. Incidentally, the spacers can be designed in any desired shape, e.g. as polyhedrons, and can be disposed in a regular or irregular distribution over the surface of the separator material. They must be electric insulators and must be resistant against acid.
The spacers can be built into the separator material, e.g. by extruding plastic particles into it or, e.g. by local injection of binders which subsequently harden in the separator material. From the point of view of production engineering, the inclusion of the spacers in the separator material is especially simple if it is accepted that the support surfaces of the spacers on one side of the separator material lie flush in the surface of the separator material. In this case, the spacers can simply be sludged in, e.g. when the fleeced strip material is being fabricated.
Building in the spacers also decisively improves the mechanical loadability of the separator material, which generally is produced as rolled goods. The separator material is formed from microfibers in the form of a fleece and receives a certain strength, e.g. by extruding the plastic particles into it or by injecting binders. Thus, it is easier to handle during the production operation and does not tear so easily, e.g. when it is pulled off the roll.
The spacers can be connected together within the separator material, e.g. like beads on a string. This results both in fixing the position of the spacers and also in improving the mechanical loadability of the separator material.
An especially advantageous embodiment of the invention provides that the spacers which are built into the separator material during the preliminary production stage thereof are fixed in position by a net or a screen which preferably is very thin and wide-meshed. This can be done during the preliminary production stages of the separator material, e.g. by spinning a fleece of microfibers about a net or screen, at whose crossing points the spacers are disposed and are attached to the net or screen. Such nets or screens, which preferably are very thin and wide-meshed, and which extend in the transverse and longitudinal direction of the separator material, hinder neither oxygen diffusion to the negative plate nor the electrolyte take-up capacity of the separator material. But, in addition to fixing the position of the spacers, they simultaneously have the important advantage that the finefibered mats or fleeces of microfibers, which intrinsically can withstand almost no mechanical stress, now are indeed able to accept adequate tensile forces in the plane of their surface extent. Handling a separator material that has been finished in this way thus becomes much simpler. For instance, the separator material can be pulled directly off the roll during automatic production of the storage batteries, without the rolls themselves requiring an expensive and controlled drive, which previously had to be regarded as necessary to prevent the easily destroyed separator material from tearing. Now, despite the fact that the separator material is handled under tensile stress during the production of the storage batteries, an undisturbed connected and closed structure of the separator material between the electrode plates can be guaranteed, a structure that is free from internal cracks or deformations and which thus guarantees high-power and shortcircuit-free operation of the inventive storage batteries.